The present disclosure relates generally to pressure/flow control systems and methods for use in treating a medical condition. In some instances, embodiments of the present disclosure are configured to be part of an IOP control system for the treatment of ophthalmic conditions.
Glaucoma, a group of eye diseases affecting the retina and optic nerve, is one of the leading causes of blindness worldwide. The tissue pressure of the intraocular contents is called the intraocular pressure (IOP). Most forms of glaucoma result when IOP increases to pressures above normal for prolonged periods of time. IOP can increase due to high resistance to the drainage of the aqueous humor relative to its production. Left untreated, an elevated IOP causes irreversible damage to the optic nerve and retinal fibers resulting in a progressive, permanent loss of vision. This may be due to a direct effect of the raised pressure upon the optic nerves and/or the effect of chronic under-perfusion of the nerve head.
The eye's ciliary body continuously produces aqueous humor, the clear fluid that fills the anterior segment of the eye (the space between the cornea and lens). The aqueous humor flows out of the anterior chamber (the space between the cornea and iris) through the canalicular and the uveoscleral pathways, both of which contribute to the aqueous drainage system. The orbital globe of the eye is an essentially non-compliant sphere, allowing IOP to be influenced by a change in volume of the contents of the orbit, including both the anterior segment and the posterior segment. Thus, the delicate balance between the production and drainage of aqueous humor can influence the IOP of the eye.
FIG. 1 is a diagram of the front portion of an eye 10 that helps to explain the processes of glaucoma. In FIG. 1, representations of the lens 110, cornea 120, iris 130, ciliary body 140, trabecular meshwork 150, Schlemm's canal 160, the anterior segment 165 including both the anterior chamber 170 and the posterior chamber 175, the posterior segment 178, the sclera 180, the retina 182, the choroid 185, the limbus 190, the suspensory ligaments or zonules 195, the suprachoroidal space 200, and the conjunctiva 202 are pictured. Aqueous fluid is produced by the ciliary body 140, which lies beneath the iris 130 and adjacent to the lens 110 in the anterior chamber 170 of the anterior segment of the eye. This aqueous humor washes over the lens 110 and iris 130 and flows to the drainage system located in the angle of the anterior chamber 170. The posterior segment 178 is filled with a gel-like substance called vitreous humor. Normal regulation of IOP occurs chiefly through the regulation of the volume of aqueous humor. Similarly, however, changes in the volume of fluid (e.g., vitreous humor) within the posterior segment can affect IOP.
After production by the ciliary body 140, the aqueous humor may leave the eye by several different routes. Some goes posteriorly through the vitreous body behind the lens 110 to the retina, while most circulates in the anterior segment of the eye to nourish avascular structures such as the lens 110 and the cornea 120 before outflowing by two major routes: the conventional outflow pathway route 205 and the uveoscleral outflow route 210. The angle of the anterior chamber 170, which extends circumferentially around the eye, contains structures that allow the aqueous humor to drain. The conventional outflow pathway (or trabecular meshwork) route is the main mechanism of outflow, accounting for a large percentage of aqueous egress. The route extends from the anterior chamber angle (formed by the iris 130 and the cornea 120), through the trabecular meshwork 150, into Schlemm's canal 160. The trabecular meshwork 150, which extends circumferentially around the anterior chamber 170, is commonly implicated in glaucoma. The trabecular meshwork 150 seems to act as a filter, limiting the outflow of aqueous humor and providing a back pressure that directly relates to IOP. Schlemm's canal 160 is located just peripheral to the trabecular meshwork 150. Schlemm's canal 160 is fluidically coupled to collector channels (not shown) allowing aqueous humor to flow out of the anterior chamber 170. The arrows 205 show the flow of aqueous humor from the ciliary bodies 140, over the lens 110, over the iris 130, through the trabecular meshwork 150, and into Schlemm's canal 160 and its collector channels (to eventually reunite with the bloodstream in the episcleral vessels (not shown)).
The uveosceral route 210 accounts for the major remainder of aqueous egress in a normal eye, and also begins in the anterior chamber angle. Though the anatomy of the uveoscleral route 210 is less clear, aqueous is likely absorbed by portions of the peripheral iris 130, and the ciliary body 140, after which it passes into the suprachoroidal space 200. The suprachoroidal space 200 is a potential space of loose connective tissue between the sclera 180 and the choroid 185 that provides a pathway for uveoscleral outflow. Aqueous exits the eye along the length of the suprachoroidal space to eventually reunite with the bloodstream in the episcleral vessels.
One method of treating glaucoma includes implanting a drainage device in a patient's eye. The drainage device allows fluid to flow from the interior of the eye (e.g., from the posterior segment to a drainage site, relieving pressure in the eye and thus lowering IOP). The system and methods disclosed herein overcome one or more of the deficiencies of the prior art.